In fields where higher design characteristics are required, such as light covers and front face plates of various displays, it is demanded to impart antireflection performance to these final manufactured products in order to reduce “background reflections”. In applications for which reduction of background reflections is desirable, such as displays and lenses, various antireflective technologies have been applied; however, there is a problem that deployment of such technologies on curved surfaces or complicated shapes is difficult.
Regarding related art technologies, there is known a technology of preventing reflection by subjecting surfaces of final manufactured products to a multilayer coating obtained by laminating a high refractive index resin and a low refractive index resin; however, it is very difficult to apply this antireflective technology based on multilayer coating to curved surfaces or complicated shapes.
On the other hand, it is known that a microrelief structural body having a microrelief structure, in which minute-sized concavities and convexities are regularly arranged on the surface, exhibits antireflection performance by continuously changing the refractive index. In order for a microrelief structure to exhibit satisfactory antireflection performance, it is necessary that the interval between adjoining convexities or concavities be of a size less than or equal to the wavelength of visible light. When such a microrelief structure is applied to the surface of an object such as a display or a lens, satisfactory antireflection performance can be imparted to these final manufactured products. It is also known that such a microrelief structural body exhibits super water-repellent performance due to the lotus effect.
Regarding the method for producing a microrelief structural body, a method of disposing an active energy ray-curable composition between a mold and a light-transmissive base material, curing the active energy ray-curable composition by means of irradiation of active energy radiation, thereby transferring the concavo-convex shapes of the mold, and then detaching the mold; a method of transferring the concavo-convex shapes of a mold to an active energy ray-curable composition, subsequently detaching the mold, and then curing the active energy ray-curable composition by irradiating the composition with active energy radiation; and the like are known. However, it is not easy to obtain antireflection performance by providing the aforementioned microrelief structure on the surface of a manufactured product having a complicated shape, and there is also a problem in view of production cost.
On the other hand, as a method for imparting designability, weather resistance, scratch resistance and the like to the surface of a molded body having a complicated shape, there is known a method of laminating a decorative sheet on the surface of a molded body. Examples of the method for forming such a decorative resin molded body having a decorative sheet laminated on the surface, include an insert molding method of having a decorative sheet molded in advance into a three-dimensional shape using a vacuum molding mold, inserting the molded sheet into an injection molding mold, injecting a resin material in a fluid state into the mold, and thereby integrating the resin material and the molded sheet; and an injection molding with simultaneous decorating method of integrating a decorative sheet that has been inserted into a mold at the time of injection molding, with a molten resin that has been injected into the cavity, and thus decorating the surface of the resin molded body.
Therefore, in the case of imparting the aforementioned performances (for example, designability, weather resistance, and scratch resistance) other than antireflection performance to the surface of a molded body, it is necessary to perform three-dimensional molding such as insert molding or press molding, and a sheet and a film which can be molded by such three-dimensional molding are desired.
The antireflective film with multilayer coating described above exhibits antireflection performance by precisely controlling the refractive indices and thicknesses of various layers, and therefore, when such a film is used in three-dimensional molding such as insert molding or press molding, there is a problem that the intrinsic antireflection performance cannot be sufficiently exhibited.
Patent Documents 1 and 2 disclose methods for producing an antireflective article having a microrelief structure on the surface, by providing a microrelief structure on the surface of a template having a curved surface, and performing press molding or injection molding.
In these methods described in Patent Documents 1 and 2, an intended microrelief structure can be provided to a molded body by providing a reverse structure of a microrelief structure in the mold; however, it is difficult to form a reverse structure of an intended microrelief structure in the mold, and since it is a premise that a molten resin that can be injection molded is used, it is very difficult to impart functions other than the antireflection performance.
Furthermore, in a case in which the microrelief structure described above is used for three-dimensional molding, the microrelief structure has inferior scratch resistance compared to molded bodies such as a hard coat having smooth surface that has been produced using the same curable composition, and therefore, a molded body laminated with the microrelief structure has a problem with durability during use.
Patent Document 3 discloses that from the viewpoint of scratch resistance, it is preferable that the cured resin that constitutes a microrelief structure has a high elastic modulus.
Furthermore, in a structure in which micro-convexities are arranged to stand close together, when the aspect ratio of the micro-convexities is high, and the elastic modulus of the cured resin is low, a phenomenon in which adjacent convexities draw close together may occur. An aggregate of convexities that have drawn close together may be considered as one large convexity; however, it is known that when the aggregate of convexities acquire a size equivalent to the wavelength of visible light, diffuse reflection of light occurs, so that the microrelief structure turns cloudy and has a high haze value. That is, in a case in which a cured product of an active energy ray-curable composition used for the production of a microrelief structure is not sufficiently solid, there occurs a phenomenon in which convexities of micro-concavo-convex shapes draw close together as a result of release from the template or heating, and as a result, there is a problem that the antireflection performance is deteriorated.
From these reasons, regarding the curable composition for forming a microrelief structural body, it is general to use a curable composition which gives a cured product having a high elastic modulus, so as to avoid close drawing of convexities and an increase in the haze value, while maintaining the antireflection performance. However, such a curable composition gives a cured product that lacks “elongation”, that is, lacks “stretchability”. Therefore, it is impossible to perform the three-dimensional molding previously mentioned.
When a microrelief structural body is formed using a curable composition which can give a cured product having excellent flexibility and stretchability, it is possible to use the microrelief structural body for three-dimensional molding; however, the phenomenon in which convexities draw close together occurs, and the antireflection performance is impaired. For example, when a microrelief structural body is formed using a curable composition including a bifunctional monomer and a hexafunctional oligomer as described in Patent Document 4, convexities draw close together and grow into a size capable of scattering light, and the microrelief structural body acquires a cloudy external appearance.